Use of freestanding nitride veneers in semiconductor devices

ABSTRACT

Thin freestanding nitride veneers can be used for the fabrication of semiconductor devices. These veneers are typically less than 100 microns thick. The use of thin veneers also eliminates the need for subsequent wafer thinning for improved thermal performance and 3D packaging.

REFERENCE TO PRIOR APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/572,770, which was filed on Jul. 21, 2011, whichis herein incorporated by reference.

BACKGROUND OF THE INVENTION

Silicon semiconductor devices are typically manufactured in wafer formdue to the availability of boule growth processes for silicon and otherpopular semiconductor devices. Nitrides however lack a suitable low costnative substrate. Even if such wafers were available polishing to an epiready surface is problematic due to variable miscut angles, surfacedefects, and low etch rates. The difficulty in polishing especially highquality HVPE nitride surfaces is discussed by DenBaars in ChemicalMechanical Polishing of Gallium Nitride (2002). As such considerableefforts have gone into growing nitrides on non-native substrates such assapphire, silicon, silicon carbide and glass. The quality of devices isalways compromised when non-native substrates are used. Latticemismatches between the non-native substrate and nitride layer inducesinternal stresses, limits subsequent process temperature ramp rates, andeven decreases growth rates of subsequent layers. Device designs arealso limited by the presence of a non-native substrate. This leads toadditional processing steps such as transfer processes like laserliftoff or multiple etching steps to expose under-lying layers forinterconnect and thermal performance reasons. In addition, polarizationeffects can play a significant role in device performance. The stressescreated by the lattice mismatch between the non-native substrate andnitride layer have been shown to affect virtually every deviceperformance parameter ranging from high current droop to indiumincorporation. Lastly, the use of non-native substrates limitssubsequent epitaxial growth processes due to a tendency for wafers tocrack or shatter during the rapid thermal changes required for devicegrowth. The need therefore exists for novel methods and devices whichovercomes these limitations.

Thick (>5 mm) freestanding nitride wafers up to 2 inch in diameter havebeen grown in the prior art but are extremely expensive and typicallyhave a large number of cracks and other defects. To obtain thin slicesfrom this thick boule they must be mechanically sawed. The slicingprocess introduces defects due to misalignment to the crystal planes. Inaddition the polishing steps required to create an epitaxial surfaceintroduces defects and requires several hours of polishing. The bulknitride boule is also significantly bowed at room temperature. Cuttingflat wafers from this growth causes a variable miscut across each wafersliced from the boule. This causes the electrical or optical propertiesof devices grown on these nitride wafers to vary based on their locationacross the wafer. An example of diced wafers from boule growth can beseen in Dmitriev Pat. Appl. 20060280668. In Dmitriev AlN boules aregrown greater than 5 mm thick and then diced and polished to create awafer greater than 6 cm in diameter. Polishing defects and variablemiscut angle defects are inherent to this prior art process. The needexists for a low cost freestanding substrate which does not requireslicing or polishing and its inherent defects but has sufficientmechanical integrity for further processing and handling. Highpressure/High temperature growth methods for GaN boules suffer from thesame cutting and polishing issues as HVPE based boules but also sufferfrom contamination issues as well which can negatively impact theabsorption or alpha coefficient of the material. In general, high alphaleads to high optical absorption losses which further illustrates theneed for an economical source of thin nitride growth substrates.

In many devices the need also exists for access to both the front andback of the nitride layer. Multi junction solar cells would especiallybenefit from the ability to grow/deposit semiconductor layers on bothsides of a thin nitride low defect veneer. Used for optical devicefabrication nitrides can span a significant portion of the visiblespectrum. With high doping concentrations InN has been shown to exhibita bandgap of 0.7 eV, however to achieve this high doping concentrationvery pure and very low defect Gallium Nitride is required. High qualityhigh indium composition InGaN is difficult to grow. Typically this isdone with expensive and tedious processes like molecular beam epitaxy(MBE). These processes cannot be scaled up to achieve a high throughputlow cost means of production. Therefore a need exists for a low cost andviable process to produce low cost high quality nitrides which do nothave to be sawed and polished and have low stress and low defectdensities and can accept high doping concentrations dopants (e.g.Indium).

Another very prevalent problem of growing nitride layers on thicksubstrate templates is stress and warping induced by the difference inthermal expansion of the two layers. As an example a typical 30 micronGaN on thick (440 μm) sapphire 2 inch diameter template will bow over200 microns either at room temperature or at growth temperature. If thebow is present at room temperature, formation of contacts and liftoffprocesses exhibit low yield due to the non-flat nature of the template.If the bow is present during growth processes, non-uniform heating istypically experienced which results in variation of devicecharacteristics (e.g. greater than 100 nm of variation in peakwavelength output has been seen for 30 micron templates on sapphire).The stresses induced due to the mismatch of thermal expansioncoefficients result in limitations on doping concentrations attainable.For example GaN layers under stress during doping will accept lowerconcentrations of dopants (e.g. Indium).

As detailed above nitride templates exhibit significant bow either atroom temperature or growth temperature which reduce yield. Thesetemplate approaches are also sensitive to rapid thermal transients whichlimit reactor processing conditions. For example nitride films on thickforeign substrates will crack if thermal cycled at too rapid of a rate.Bulk nitride approaches besides being cost prohibitive, exhibit surfacedefects due to polishing and have a variable miscut across the waferwhich leads to variation in the device performance across the wafer.Therefore a need exists for an improved method of growing nitride layersthat are stress free, can absorb dopants, are not sensitive to crackingduring fast thermal cycling, can be uniformly heated and are economicalto produce.

As discussed above, conventional nitride growth substrates in all formssuffer from significant internal stresses. As such a number ofprocessing constraints are placed on the growth reactors used to makedevices on these nitride growth substrates. The nitride veneersdisclosed in this filing do not have the same processing constraints asthe existing nitride growth substrates listed above. As such the needexists for a growth reactors which can take advantage of the improvedprocessing conditions offered by nitride veneers.

SUMMARY OF THE INVENTION

Thin veneers of nitrides, devices formed on thin nitride veneers,methods of forming thin nitride veneers and methods of forming deviceson thin nitride veneers are embodiments of this invention. The use ofthese veneers as subsequent growth substrates is disclosed. The use offlexing means to modify the stress profile in the veneer during or aftersubsequent processing steps is also disclosed. The use of this techniqueto enhance electron/hole overlap in quantum well structures is apreferred embodiment of this invention. The growth of a substantiallydifferent bandgap material on a nitride veneer is an embodiment of thisinvention. The use of a dilute nitride buffer layer between the nitrideveneer and a substantially different bandgap material is an embodimentof this invention. The use of annealing process including but notlimited to rapid thermal annealing and laser annealing prior to or afterdeposition of a substantially different bandgap material in a controlledatmosphere is also disclosed.

The ability to grow silicon, Si/Ge, and other low bandgap materials onnitride veneers is disclosed in this invention, as well as the use ofthese materials in multi-junction devices such as solar cells. Usingthis approach high quality nitride solar cells tuned to shortwavelengths of the solar spectrum can be combined with efficient red andIR solar cells in a cost effective manner. The growth of low bandgapmaterials on nitride veneers is an embodiment of this invention. Usingthis approach, this invention enables the integration of a wide range ofsemiconductors using a thin nitride veneer as the growth substrate. Theflexible nature of the freestanding nitride veneer allows for stressrelief during and after growth. Unlike bulk thick nitride wafers,flexible veneers allow for compensation of crystal lattice mismatch.Unlike template or engineered substrates the nitride veneer layerdisclosed is not restrained and can therefore flex as needed tocompensate for mismatches between the layers. Direct epitaxial growth oflayers with very large lattice mismatches have been demonstrated onfreestanding nitride veneers.

The intent of this invention is to disclose the use of thin freestandingnitride veneers for the fabrication of semiconductor devices. Theseveneers are typically less than 100 microns thick. The use of thinveneers also eliminates the need for subsequent wafer thinning forimproved thermal performance and 3D packaging. In vertical devices theseries resistance and thermal resistance is directly proportional to thethickness of the device. Most preferred are veneers with a thicknessbetween 20 microns and 100 microns. Even more preferred are nitrideveneers with a thickness between 30 microns and 75 microns. The bulkthermal conductivity of GaN is between 120 and 200 W/m·K depending oncrystal quality with an estimated theoretical maximum thermalconductivity of up to 400 W/m/K. A typical LED device can generateseveral watts of heat per mm2. A bulk wafer 300 microns thick has 6times the thermal resistance of a 50 micron thick nitride veneer. Assuch, in bulk wafers thinning techniques are required to make usefuldevices. Nitride veneers eliminate the need for thinning and waferbonding processes.

The veneers disclosed are flexible in nature and are substantially allnitride in composition. This then eliminates the requirement to usenon-native substrates with all their attendant deficiencies. Thesubstantially homogenous nature and low thermal mass of the freestandingnitride veneers allow for the use of epitaxial growth methods whichexhibit rapid thermal temperature changes as required for devicesincluding but not limited to quantum wells, solar cells, laser diodes,sensors, and electronic devices (HEMTs, FETs, etc.). This enables theuse of rapid heating and cooling techniques within the reactor which inturn allows for much tighter controls of compositions within thinlayers. The use of veneers in HYPE, MOCVD, MBE, ALD as well as othergrowth processes as known in the art is an embodiment of this invention.The use of these thin veneers as growth substrates for enhancedcomposition control of thin layers is a preferred embodiment of thisinvention.

The use of thin veneers offers several advantages over polished wafersand thick nitride templates grown on non-native substrates. In the caseof polished wafers, the polishing process introduces a large number ofdefects into the substrate surface. The stress profiles within thepolished wafers are also much higher than the thin veneers disclosed inthis invention. Polished wafers are typically cut from 1 cm thick HVPEgrowth on sapphire or some other non-native substrate. This is verycostly process and yields only a limited number of wafers per run.Unlike polished wafers, the veneers disclosed in this invention canexhibit at least one epi-ready surface which requires no furtherpolishing steps before growth. As stated earlier, the stress within theveneer is much lower and can be adjusted by flexing the veneer duringsubsequent growth steps. In this manner, the spontaneous and inducedpolarization fields within the finished devices can be modified. Withrespect to thick nitride templates, veneers are freestanding and can gothrough very rapid temperature changes without cracking. This isespecially critical in the formation of MQWs and other thin layereddevices. In addition the flexible nature, high thermal conductivity,thinness of the freestanding nitride veneers allows for more uniformheating during subsequent device growth steps.

The veneers cited in this disclosure are harvested freestanding nitridelayers from thick HVPE templates specifically engineered for the lowalpha within the visible wavelength region. Typically the layers arebetween 20 and 150 microns thick and even more preferable between 30 and100 microns thick. Undoped, n doped, semi-insulating, and p doped layersare disclosed. The doping may be uniform or graded through the layer.While polar C plane with less than 1 degree off cut is preferred, othercrystal orientation including semi-polar and non-polar are disclosed.These layers are flexible and epi-ready as harvested using the patentedlaser liftoff approach referenced and part of this disclosure U.S.patent application Ser. Nos. 2009-0140279; 2010-0032682; and2010-0060553, commonly assigned and herein incorporated by reference.These flexible freestanding foils are then used directly without anyfurther processing steps to generate the devices disclosed in thisfiling.

Unlike GaAs, GaN can be handled in very thin layers. Even thoughdislocations densities are high, veneers of GaN between 20 and 150micron which are flexible and crack free can be formed by a variety ofmethods including but not limited to laser liftoff, chemical etching,use of a mechanically weak interface, and photochemical means. Whiletemplates with reasonable thickness have been grown by several groups,not all growths are suitable for thin veneers. Stress profiles withinthe layer are very critical for the formation of robust thin veneers. 30micron thick layers with a surface area greater than 1 inch square havebeen harvested. With the use of proper fixtures, these thin layers canbe mounted for regrowth, coating, annealing, stacked, and printed onwithout damage. A key attribute of these thin veneers are that thinningtechniques are not required to create thin die with enhanced optical,thermal, and electrical performance. An embodiment of this invention isa nitride veneer with thickness between 20 microns and 150 microns whichcan be handled freestanding with a surface area greater than 0.5 cm².More preferably a freestanding nitride layer with a thickness between 30and 100 microns with a surface area greater than 1 cm² is disclosed. Theshape of the freestanding nitride veneer can be used to determine thebow characteristics of the veneer and which stress plane is relaxed orstressed. What is apparent is that the surface stress of the veneer isreduced by the separation from the growth substrate as indicated by thebow. This unique feature of the veneers is believed to be the reasonbehind the observed improvements in subsequent growth crystal qualityand higher indium incorporation. The anisotropic stress pattern in asquare freestanding nitride layer with one edge parallel to the flat ofa standard C plane sapphire wafer from which it was grown tends tocreate a uniaxial bow which can be used to help in mounting in a mannersimilar to a leaf spring. The use of this attribute to enable mountingin a reactor or other subsequent processing equipment is an embodimentof this invention. Subsequent growths and processes which take advantageof the flexible nature of the freestanding nitride veneer to flex, bow,twist, vibrate, and distort before, during, and after processing is apreferred embodiment of this invention.

Stress on a surface has been shown to modify the composition andstructure of subsequent growths. Not only are nitrides anisotropic andpiezoelectric in nature, but their lattice constants vary significantlywith pressure. The interaction of and effects of internal piezoelectricfields both static and transient are the subject of intensive researchas these fields can effect current droop, gain (both optical andelectrical), resistivity, as well as basic properties such as hole andelectron mobility. The flexible nature of the freestanding nitrideveneer allows relaxation and/or strain of the various crystal planeswhich can be used to modify the properties of both the freestandingnitride films and/or subsequent growths. As such the flexing of nitrideveneers to enhance, change, and/or substantially modify the propertiesof subsequent growth processes is a preferred embodiment of thisinvention. The nitride veneer may be flexed via mechanical means,electrostatic means, gas pressure, magnetic fields, and spatiallyvarying heating via actinic radiation. The use of actinic radiation tomodify, clean, etch, pattern and diffuse species into the nitride veneeris also disclosed. The use of LPE, electron beam, ion beam, and otherdiffusion based approaches as known in the art to modify, introduce aspecies, clean, and bond onto or into a nitride veneer is alsodisclosed.

A preferred method of forming the nitride veneer is based on laserliftoff of HVPE grown nitride layers from sapphire wafers as disclosedpreviously by the authors and included by reference. Critical to thisprocess is the surface quality and crack free nature of the growth priorto liftoff. Alternately, the use of mechanical separation, chemicalseparation, photochemical separation, and/or use of a sacrificial growthsubstrate that is subsequently etched away is included as reference.HVPE is the preferred method of formation based on crystal quality, lowalpha, and surface quality. The nitride veneers maybe doped, undoped, orsemi-insulating in nature. The use of gradient doping, step doping, oruniform doping in the nitride veneer is also disclosed. Theincorporation of an epitaxially grown stress skin on nitride layer priorto separation to enhance the robustness of the nitride veneer is anembodiment of this invention. The nitride veneer may consist of anydilute nitride including but not limited to GaN, AlGaN, InGaN, AlInGaN,as well as alloys of As and P. Most preferred are GaN doped with atleast one of the following dopants, Si, Zn, Mg, Ga, Al, and rare earths.Dopants may be used to impart conductivity, semiconducting, and/orluminescent properties to the nitride veneers. Luminescent nitrideveneers are an embodiment of this invention. The use of luminescentveneers as wavelength converters, gain media, and/or sensors is anembodiment of this invention.

Also disclosed is a rapid thermal growth reactor which takes advantageof the low thermal time constant of the nitride veneer. The thermal timeconstant of a material is directly related to the volume of materialused. In any device growth layer thickness control and the interfacebetween individual layers is determined by how quickly reactor processconditions can be changed. As an example, a typical quantum well in theblue led is 30 Angstroms thick. As such conventional nitride growthreactors must use very low growth rates and MO sources to resolve thesethin layers and create reasonable interfaces between the layers. Atypical LED MOCVD growth process can be up to 8 hours. Not only doesthis increase device cost but the extended growth cycle increasessusceptibility to power interruptions and mechanical failures. The useof the nitride veneers disclosed in this filing allows for a whole newclass of reactor designs which take advantage of the low thermal timeconstant of the nitride foils. The low thermal time constant of thefreestanding nitride veneers disclosed enable heating rates in excess of1000 C/sec and cool down times on the msec time scale. In order to takeadvantage of these benefits the reactor must use rapid heating methodsincluding but not limited to direct heating of the nitride veneers vialaser or other actinic radiation, process gas valves and flow ratesensors with millisecond response times, low volume reaction chambers,and control systems with millisecond response times. A preferredembodiment of this reactor is based on halide based sources such as butnot limited to InCl3 and GaCl3. The high growth rate and high purity ofthese sources on nitride veneers allow for LED growth cycles of lessthan 30 minutes. The use of ALD is a preferred method of operation forthis reactor. InCl3 sources must be heated to up to 300 C to providesufficient vapor pressure for high deposition rates as such the use ofhigh temperature ALD valves as produced by Swagelok in a rapid thermalnitride ALD reactor is a preferred embodiment of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a nitride template on sapphire.

FIGS. 2A and B depicts a freestanding nitride veneer.

FIG. 3 depicts a freestanding nitride veneer with at least oneadditional semiconductor layer.

FIG. 4 depicts a freestanding nitride veneer with a buffer layer.

FIG. 5 depicts a freestanding nitride veneer with a buffer layer and lowbandgap coating.

FIG. 6 depicts a multi junction solar cell based on nitride veneer withsilicon junction.

FIG. 7 depicts a process for making integrated multijunction solar cellsusing nitride veneers.

FIG. 8 depicts a LED array with a silicon actively addressed matrixgrown on a nitride veneer.

FIG. 9 depicts stacked multi junction devices based on nitride veneers.

FIG. 10 depicts a flexed veneer during subsequent growth.

FIG. 11 depicts high temperature contacts formed on nitride veneers.

FIG. 12 depicts a rapid thermal process reactor designed for nitrideveneers.

FIG. 13 depicts modification of the surfaces of nitride veneers.

FIG. 14 depicts implantation of dopants using nitride veneers.

FIG. 15 depicts a luminescent nitride veneer.

FIG. 16 depicts a solid state diode pumped doped nitride veneer laser.

FIG. 17 depicts HEMT formed on nitride veneer.

FIG. 18 depicts a 3 dimensional stack of nitride veneers.

FIG. 19 depicts a flexible nitride veneer mounted to the outer surfaceof round heatpipe.

FIG. 20 depicts an integrated biosensor based on a freestanding nitrideveneer.

DETAILED DESCRIPTION OF DRAWINGS

FIG. 1 depicts a prior art typical template. Non-native growth substrate1 may include but not limited to sapphire, SiC, Si, and glass. Anucleation layer 2 may be used to initiate growth and compensate forlattice mismatches. In the case of sapphire non-native growth substrates1 nucleation layer 2 may include but not limited to low temperature GaN,AlGaN, AlN, ZrB2, as well as other buffers known in the art. Nitridelayer 3 is typically 2 to 5 microns thick due to stresses induced due tothe lattice mismatches between the nitride layer 3 and non-native growthsubstrate 1. Nucleation layer 2 may also provide a weak mechanicalinterface via a porous nature and/or chemical suspectibility to allowfor selective chemical etching. A preferred method of removal is vialaser liftoff as disclosed previously. In order to compensate for thelattice mismatches dislocations 4 occur within nitride layer 3. It iswell known within the art that the density of these dislocations 4decrease with increased nitride layer 3 thickness. The stress profilebetween surface 6 and surface 5 can be varied based on growthconditions. One of the fundamental problems with template basedapproaches is the bow created by the lattice mismatch between thenitride layer 3 and non-native growth substrate 1. Depending on growthconditions and the use of stress control layers the template can bevirtually flat at room temperature or strongly bowed. However a templatewhich is flat at room temperature will be bowed at growth temperatureand vice versa for the template which is bowed at room temperature. Thisis also difficult to control especially for thick template growths. Tocomplicate things further the coefficient of thermal expansion versustemperature curves are typically different for the non-native substrate1 and nitride layer 3. This dramatically limits the temperature ramprates of any process using the template approach. This is especiallytrue for templates greater than 10 microns in thickness and wafersgreater than 2 inch in diameter. This has led to yields of less than 50%for 4 inch wafers even with nitride layers 3 of only a few microns. Thetypical failure mechanisms are epi layer cracking and/or delamination,or cracked templates. Since typically high rotational speeds are used onthe platens in nitride reactors, cracked templates can fly within thereactor leading to extensive damage of the reactor itself not to mentionyield losses. The stresses at surface 5 can also affect the rate ofgrowth especially in the case of InGaN. For these reasons as well asothers the use of a freestanding nitride veneer as disclosed within thisinvention is distinctly advantageous over a template based approach.

FIG. 2A depicts a freestanding nitride veneer 7. This layer ispreferably between 20 and 150 microns thick with a surface greater than0.5 cm2. Even more preferably the freestanding nitride veneer 7 isbetween 30 and 100 microns thick and greater than 1 cm² in area.Freestanding nitride veneer 7 maybe doped, undoped, or semi-insulating.Gallium nitride is a preferred embodiment, however all dilute nitridesare also embodiments of this invention. Freestanding nitride veneer 7maybe be doped with a variety of materials including but not limited toSi, Mg, Zn, Ga, Fe, and rare earths. These dopants maybe uniformly ornon-uniformly doped into the freestanding nitride veneer 7. The dopantlevels maybe up to and including degenerative levels. The dopants may beused to impart conductivity, semi-insulating and/or luminescentproperties to the freestanding nitride veneer 7. The use of LPE, ionimplantation, thermal diffusion as well as other doping methods as knownin the art to create at least a region of doped nitride material withinone side, both sides, or the entire thickness of freestanding nitrideveneer 7 is disclosed. Surface 9 is typically the side which wasattached to the non-native growth substrate which as such tends to havethe higher dislocation density. Surface 9 is typically textured due tothe liftoff process and may include part of the nucleation layerdescribed previously. The texturing of surface 9 to enhance lightextraction, control stress, prescribed for subsequent cleavingoperations, and texturing for enhanced regrowth are all embodiments ofthis invention. The use of excess gallium formed during separationespecially laser liftoff as a dopant for subsequent growth is also anembodiment of this invention. Typically the stresses found withinfreestanding nitride veneer 7 leads to a uniaxial bow which aligns toone of the crystal planes. FIG. 2B depicts a square freestanding nitrideveneer 11 in which a cleavage plane is substantially oriented to oneedge of the square freestanding nitride veneer. Alternately, atriangular freestanding nitride veneer is disclosed whereby threecleavage planes are substantially oriented to three edges of thetriangular freestanding nitride veneer. In this configuration stressesare balanced leading to cup shaped bow across the freestanding nitrideveneer 11. Hexagon, parallelograms, and other shapes that can be formedbased on equilateral triangles are also disclosed. The use of shape totailor bow and stress within freestanding nitride veneer 11 are alsodisclosed. In particular the use of shape to create non-flat layers withmodified stress profiles to enhance mounting and/or improve performanceof devices formed on freestanding nitride veneer 11 is disclosed. Whilec plane nitrides are a preferred embodiment the formation offreestanding nitride veneers 11 on other crystal planes are alsodisclosed. The preferred shape of the freestanding nitride veneer 11would be adjusted to account for the new cleavage planes created by thenew crystal plane orientation and is an embodiment of this invention. Ingeneral, the combination of thickness, crystal orientation, and shape isdisclosed as a method of modifying the stress profile within nitrideveneers. The formation of layered structures with substantially similar,opposite, and/or different thicknesses, crystal orientation, and shapeto create a particular stress profile within at least one of the layersis disclosed. A preferred embodiment is that at least one of theselayers be a freestanding nitride veneer 11. Semiconducting andnon-semiconducting materials including, but not limited to, polymers,metal, semiconducting layers (silicon, etc.) and dielectrics. The use ofdirect waferbonding, adhesive bonding, and/or high temperature glassfrits to adhere at least on nitride freestanding veneer 11 to anotherlayer is disclosed. Formation of stacked freestanding nitride veneers 11for 3 dimensional packaging is disclosed. The use of this technique tocreate optoelectronic packages which take advantage of the opticaltransmittance of at least one freestanding nitride layer 11 in the3-dimensional packages is a preferred embodiment. The attachment oftemporary films polymeric, glass, metals, or semiconductor layers forhandling, induce a bow, and/or enable subsequent processing steps isalso disclosed. The application of a photoimagible film to at least oneside of freestanding nitride veneer 11 is a preferred article of thisinvention.

FIG. 3 depicts a freestanding nitride veneer 12 with at least oneadditional layer 13. Additional layer 13 may consist of but not limitedto an organic or inorganic material. Preferably additional layer 13 mayconsist of but not limited to metal, dielectric, and/or semiconductinglayer. More preferably, said additional layer 13 may be a layerdeposited by but not limited to sputtering, LPE, MBE, MOCVD, HYPE, ALD,evaporation, spraying, dip coating, printing, and/or spin coating. Theuse of conversion methods using thermal processes, actinic radiation,ion implantation, etching, chemical means using at least onefreestanding nitride veneer and at least one additional layer 13 isdisclosed. The at least one additional layer 13 may be spatially varyingor uniform. The at least one additional layer 13 may be permanent orsacrificial in nature. Surface 14 between the freestanding nitrideveneer 12 and at least one additional layer 13 maybe be either side offreestanding nitride veneer 12. The use of texturing, chemicaltreatments and/or actinic radiation means either uniformly or spatiallyvarying to adjust, enhance, modify, change the wetting characteristics,and/or roughen surface 14 is disclosed. More preferably the modificationof surface 14 to modify/enhance the adhesion, crystal quality, stressprofile, and/or transport properties between or of either at least oneadditional layer 13 and/or freestanding nitride veneer 12 is disclosed.As an example the selective etching of the nitride face of afreestanding gallium nitride veneer such that enhanced lateral growthmethods can be used to regrow via HVPE a higher crystal quality nitridelayer is disclosed. As another example the use of laser ablation to formmicrooptical CPC in the freestanding nitride veneer 12 prior todeposition of a mulitilayer dielectric mirror is disclosed. Alternately,surface 15 may be modified as well for the formation of microopticalelements, extraction means, and/or mechanical elements. The modificationof any of these layers via chemical, actinic radiation, implantation,and/or mechanical means is also disclosed. A preferred embodiment of theinvention is the formation of a freestanding nitride veneer 12 and atleast one additional layer 13 which consists of a semiconductor withsubstantially different bandgap than the freestanding nitride veneer 12.As an example at least one additional layer 13 would consist of a lowbandgap material such as but not limited to silicon, silicon/germanium,germanium, gallium arsenide, alingap, dilute nitrides, InP, antinomides,and ZnO alloys. The use of this layered material in solar cells, laserdiodes, LEDs, electronics is disclosed. More preferably the use of thislayered material in multijunction solar cells is disclosed. Because ofthe substantially single crystal nitride and mechanically flexiblenature of freestanding nitride veneer the need for buffer layers andother methods such as twist wafer bonding to enhance lattice matchingcan be eliminated. Direct epitaxial growth of substantially singlecrystal InSb on freestanding GaN veneers have been demonstrated eventhough very large lattice mismatches are present. Enhanced growth ratesand indium concentrations for InGaN based on freestanding nitrideveneers 12 have also been demonstrated due to reduced surface stressesof the veneers. Since additional polishing steps are not required bythese veneers versus bulk nitride wafers processing costs and surfacedefects can all be reduced. The epitaxial growth of but not limited tonitrides, oxides, antimonides, phosphides, diamond, silicon, si/ge,arsenides, and other semiconducting, dielectric, ferromagnetic, and/orluminescent materials with enhanced material properties relative totemplate and/or bulk nitride approaches is disclosed. The use of thehigh temperature nature of freestanding nitride veneer 12 to allow forrecrystallization, annealing, and/or modification of at least oneadditional layer 13 is disclosed. Even more preferably, the use of thethermal shock resistant nature of the freestanding nitride veneer 12 toenable rapid thermal processing of at least one additional layer 13 isan embodiment of this invention.

FIG. 4 depicts a freestanding nitride veneer 16 with a buffer layer 17.The buffer layer 17 maybe epitaxial or non-epitaxial in nature.Typically the layer is formed on surface 18 via epitaxial means butamorphous layers are also disclosed. Alloys of nitrides are a preferredembodiment with thicknesses ranging from several angstroms to a micron.Texturing, chemical modification, and actinic radiation eitheruniformily or spatial varying in nature of at least one surface ofnitride veneer 16 is disclosed. Formation of the buffer layer viadiffusional techniques as known in the art is also an embodiment. Atleast one freestanding nitride veneer 16 with a buffer layer 17 whichenhances subsequent processes and layer formation is an embodiment ofthis invention.

FIG. 5 depicts freestanding nitride veneer 19 with at least one bufferlayer 20 and at least one additional layer 21. At least one additionallayer 21 may consist of a metal, dielectric, and/or semiconductor. Evenmore preferred at least one additional layer 21 is a semiconductor witha bandgap substantially different from freestanding nitride veneer 19.The use of this layered material in semiconductor devices including butnot limited to solar cells (single and multijunction), Power devices, RFdevices, sensors, MEMS, laser diodes, spintronics, optoelectronics, andmemories is disclosed. Preferred materials for at least one additionallayer 21 include but not limited to silicon, germanium, GaAs, InP,nitride alloys, oxide alloys, dilute nitrides containing As, P, etc.,semiconducting organics, and luminescent materials which are amorphous,polycrystalline and crystalline. At least one additional layer 21 may befunction as a dielectric, semiconductor, and/or conductor.Semiconducting materials in additional layer 21 may be p type, n type,degenerative, and/or semi-insulating. The selection of buffer layer 20and/or additional layer 21 such that the stress profile in any of thelayers depicted is modified is an embodiment of this invention. Thebending of the layers relative to a particular crystal plane prior,during, and/or after growth of the at least one buffer layer 20 and/orat least one additional layer 21 is disclosed. Using this technique thestress and growth characteristics of the various layers can be modified.The use of the modified strain layers to enhance material properties isan embodiment of this invention. The use of this technique to enhancedopant concentration, decrease dislocation density, and enhance growthrates is an embodiment of this invention. More preferably, the bendingof freestanding nitride veneer 19 during formation of at least onebuffer layer 20 and/or at least one additional layer is an embodiment.Bending may be via mechanical, electrostatic, magnetic and/ornon-uniform heating means.

FIG. 6 depicts a freestanding nitride veneer 24 with at least onenitride solar junction 23 which may consist of PN, DHJ, SQW, MQW and/orquantum dot based devices. At least one nitride solar junction 23 issubstantially composed of nitrides. At least one low bandgap solar cell25 is grown on the other side of freestanding nitride veneer 24. Atleast one low bandgap solar cell 25 may consist of PN, DHJ, SQW, MQWand/or quantum dot based devices. The advantages of this approach relateto ability to grow a fully integrated structure covering the majority ofthe solar spectrum, ability to grow high temperature structures priorand/or independently of structures which require lower temperatures, andability grow higher quality low bandgap materials using freestandingnitride veneer 24 as a growth substrate. Contact layers 22 and 26 allowfor extraction of current from the device. Contact layers 22 and 26 mayconsist of but not limited to transparent conductive oxides, metaltraces, and combinations of both. The design of either and/or bothcontact layers 22 and 26 to provide antireflection, surface texturingfor enhanced absorption, and/or improved current spreading is disclosed.The device may be constructed such that light passes through such thatadditional devices can be stacked together or have one contact layeropaque and reflective such that incident light is reflected back throughthe layers for additional opportunity of conversion. Alternately, solarjunctions made using ZnO alloys may be used to replace at least onenitride solar junction 23.

FIG. 7 depicts a process for forming multijunction solar cells. In thisprocess a freestanding veneer is formed in step 27. On the freestandingnitride veneer at least one nitride solar cell is formed in step 28.This is followed by the growth of at least one low bandgap solar cell instep 29. The use of this approach enables the formation of freestandingsolar cells which can be optimized for the solar spectrum. Nitridealloys can span the majority of the solar spectrum However it isdifficult to grow high indium content devices which the efficiency and ptype properties needed. Alternately, the growth quality nitride deviceslimits the type of low bandgap materials which can be used due tolattice mismatch and temperature constraints of the low bandgapmaterials. In a typical GaN on silicon approach the quality of thedevices is limited not only the quality of the GaN which can be producedusing silicon as a growth substrate but the underlying junctions neededin the silicon solar cell are compromised by the subsequent hightemperature nitride growth. Therefore a preferred embodiment of thisinvention is the formation of at least one nitride solar cell on afreestanding nitride veneer followed by the formation of at least onelow bandgap solar cell on the freestanding nitride veneer. While asapphire growth substrate maybe used to grow the nitride solar cell thenfollowed up with a low bandgap solar cell, the sapphire substrateintroduces thermal and optical problems into the device. As statedbefore the problems associated with growing a template like this stillexist and the quality of devices is compromised. FIG. 7 also depictsGraph 30 which illustrates how the solar spectrum can be divided intotwo basic zones, with the at least one nitride solar cells optimized forefficient operation for the higher energy photons and the at least onelow bandgap solar cells optimized for efficient operation for the lowerenergy photons. The overlap is determined by the materials being used.The use of double, triple and higher number of quantum wells, quantumdots, and other solar converting devices to efficiently cover themajority of the solar spectrum for maximum efficiency is disclosed. Theuse of layer thickness control, antireflecting layers, current spreadinglayers, surface texturing, internal structures, and the use of multiplestacked devices to enhance the efficiency is also disclosed. Aspreviously disclosed by the author the use of spatially varyingcomposition and thickness within the device and spectrum splittingoptics to form a rainbow across the solar cell is also included as anembodiment.

FIG. 8 depicts an active matrix addressed freestanding nitride veneerLED array. Freestanding nitride veneer 31 contains an array of LEDs 32,which are grown on the freestanding nitride veneer 31 and segmented intoindividual elements via trenches 33 cut into the freestanding nitrideveneer 31. The thickness of the freestanding nitride veneer 31 enablesthe formation of micro CPCs which direct light from the individual LEDs32 outward. The use a barrier 34 to prevent cross talk between theindividual LEDs 32 is also disclosed. Barrier 34 maybe a metal, adielectric and/or a combination of both, in the case of the dielectricthe use of a material with a lower refractive index than thefreestanding nitride veneer 31 is preferred to enhance internalreflection of the CPC. The growth of an active matrix backplane 35 isalso disclosed which can be used to address the individual LEDs 32. Acommon contact 36 maybe formed either as shown or within the barrier 34region.

FIG. 9 depicts stacked freestanding nitride veneer based solar cells38,39,40 and 41 contained within a CPC 37. CPC 37 maybe 3 dimensional,linear, and/or approximated by a simple V shape. CPC 37 maybe air,liquid, or solid filled. Most preferably, stacked freestanding nitrideveneers based solar cells 38, 39, 40, and 41 are sandwiched within aglass CPC which provides concentration of incident solar energy andthermal cooling of the solar cells.

FIG. 10 depicts a freestanding nitride veneer 42 with uniaxial bow asdepicted. The bow is defined by the stress profile within thefreestanding nitride veneer 42. Since many of the performance parameterswithin nitride devices are determined by the spontaneous and inducedpolarization fields within the device itself flexing of the freestandingnitride veneer can be used to modify device performance. FIG. 10 alsodepicts a simple mounting fixture 43 based on using the bow of thefreestanding nitride veneer 42 to hold itself in place duringprocessing. The constrained freestanding nitride veneer 44 will exhibitdifferent properties depending on the amount, direction, and type offlex induced by the mounting fixture 43. Both static and dynamic flexingof the freestanding nitride veneer 42 is disclosed. In the case ofdynamic acoustical, piezoelectric, and capacitive means can be used tovibrate the freestanding nitride veneer 42 during subsequent processingsteps.

FIG. 11 depicts a printing process for forming ohmic contacts to nitrideveneer based devices. Freestanding nitride veneer 45 is processed tocontain semiconducting devices including but not limited to LEDs, laserdiodes, HEMTs, solar cells, and other electronic/optoelectronic devices.Thick film high temperature conductor 46 is printed on to thefreestanding nitride veneer 45 via stenciling, inkjet, and photoimagingapproaches. Curing means 47 may include any actinic radiation includingbut not limited to RF heating, IR heating, laser, and combinations ofboth. Preferred is the use of rapid thermal heating techniques IR,laser, and/or electron beam based. The freestanding nitride veneer 45enables the use of rapid thermal processing of over 1000 C/minute. Curedcontact 48 is formed after firing. A preferred material for curedcontact 48 is substantially metal contacts with high reflectivityincluding but not limited to silver, platinum, palladium and theiralloys.

FIG. 12 depicts a rapid thermal processing reactor designed forfreestanding nitride veneers 52. As stated previously conventionaltemplate based approaches for nitrides can be damaged by rapid thermalcycling. This limits both how rapidly devices can be made as well as theprecision of doping and quality of the interface between layers. Thishas a direct impact on ultimate device performance. Interfaces betweenlayers are also greatly impacted by how rapidly reactor processingconditions can be changed. As an example a horizontal reactor isdepicted in FIG. 12. Vertical and rotating designs are also embodimentsof this invention. Because freestanding nitride veneers 52 aresubstantial homogenous very rapid temperature changes are possible.Heating rates in excess of 1000° C./sec have been demonstrated. The lowthermal mass nature of freestanding nitride veneers 52 allows for veryrapid thermal temperature changes. In this reactor design IR lamps 49and 54 are used to heat freestanding nitride veneers 52 which aremounted to a thin susceptor 51. Alternatively, laser or other actinicradiation sources may be used to heat the freestanding nitride veneers52 either directly or indirectly via a coating layer on the freestandingnitride veneers 52 or via a thin susceptor 51. A preferred embodiment ofthis invention is direct heating of the freestanding nitride veneers 52via actinic radiation is disclosed. Cooling is via process gases 50contained within reactor chamber 55. The low thermal mass of thefreestanding nitride veneers 52 dramatically reduce the cooling timeconstant relative to conventional growth substrates. As the reactorchamber 55 volume must be minimized and process gases 50 flow rates mustbe maximized to take advantage of the low thermal mass of thefreestanding nitride veneers 52. Preferred is reactor chamber volume ofless than 10 cc. It is a preferred embodiment that reactor chamber 55 besubstantially transparent to the radiation emitted by IR lamps 49 and 54or other actinic radiation used to heat freestanding nitride foils 52Alternatively, the use of RF heating and an appropriate susceptor 51 isalso disclosed. The low thermal mass of freestanding nitride veneers 52and thin susceptor 51 is critical for cooling processes as well asheating processes within the reactor. Temperature control is viathermocouple 53 which controls the IR lamps 49 and 54. The use ofmultiple thermocouples 53 to control zones and/or lamps individually isalso disclosed. The use of alternate temperature sensing means includingbut not limited to band edge sensors and pyrometers is also disclosed.Thin susceptor 51 maybe be solid or contain hole whereby a substantialportion of both sides of freestanding nitride veneers 52 are exposed tothe process gases 50 and IR radiation from IR lamps 49 and 54. In thismanner both sides of freestanding nitride veneer 52 can be grown on.Direct heating of the freestanding nitride veneers 52 via actinicradiation is also disclosed. Typically MOCVD growth rates are less than1 micron/hour. However that represents 10000 angstroms/hour or severalangstroms/second. Quantum wells are typically tens of angstroms thickand consist of two or more distinctly different compositions and/ordoping levels. There can be more than 100° C. difference in theprocessing temperatures for the various layers within a device. Inaddition process gases must typically be switched to create the optimumdevice structure. The quality of the device is also determined by theinterface between the various layers. InGaN is especially susceptible tothe formation of defects and rough interfaces within MQW structures.Indium has a tendency to segregate during crystal growth which leads tocomposition fluctuations and defect formation in the thin layersrequired. The ability to rapidly change the growth temperature of thesubstrate and process gases within the reactor are critical tocontrolling the overall device structure. As an example, argon, ammonia,nitrogen, hydrogen, or combinations of carrier gases are provided atgiven pressure through a precision pressure regulator viaelectropolished stainless steel tubing into a high temperature oven zoneheated via heating means including block heaters and liquid heaterlines. Multiple high temperature oven zones may be used to providedifferent reactant to process gases 50. Each high temperature oven zoneshould be thermally isolated from each other. The high temperature ovenzone has sufficient thermal mass to equalize the temperatures of thehigh temperature ALD valves and solid metal chloride/halide sources.Optionally, integral disposable oxygen scavenger type filters with metalmesh filters are placed at the input and output of the solid metalchloride or halide sources. Examples of solid metal chloride or metalhalide sources are but not limited indium chloride, gallium chloride,aluminum chloride, indium iodide, gallium iodide, indium bromide,gallium bromide. Purity levels equal to or greater than 6N is preferred.The in-line disposable scavenger filters remove any oxygen from thecarrier gases and residual oxygen in the solid sources as well asprevent particles from entering the reactor chamber. In-situ activationof these in-line disposable scavenger filters is preferred. A typicaloperating temperature would be 300 C for InCl3 and 60 C for GaCl3 as anexample. One or more solid metal chloride or metal halide sources,carrier gases, high temperature ALD valves, in-line filters, and hightemperature oven zones can be used to create the appropriate processgases 50 to go into reactor chamber 55. Ammonia, nitrogen, hydrogen, andargon may also be digitally introduced into reactor chamber 55 via aseparate set of high temperature ALD valves. It should be noted that thetemperature of these additional process gases 50 and carrier gases usedentrain the reactants must be carefully regulated to prevent undesiredcooling of the solid metal chloride or metal halide sources, the reactorchamber 55, or the freestanding nitride veneers 52. The use of hightemperature ALD valves allow for full digital control of process gasses50 into reactor chamber 55. A typical switching time of 5 msecs ispossible with these ALD valves as such process gases 50 can beintroduced into the reactor chamber 55 as millisecond time scale burstsrather than the more conventional method of simply changing flow ratesthrough bubblers with 10 second or higher time constants. Theconventional bubblers must be allowed to stabilize due to how thecarrier gasses flow through the liquid chamber and therefore do not lendthemselves to rapid digital processes as disclosed in this filing. Inaddition, more conventional MO sources have very low vapor pressurewhich mandates very tight temperature controls (1 degree C.) on thebubblers to maintain a given concentration of reactants with processgases 50 compared to higher vapor pressure sources. Once the vapor fromthe solid metal chloride or metal halide sources have been entrainedinto the carrier gases, the resulting process gases 50 are transportedvia electropolished stainless steel tubing with a length less than 1meter to reactor chamber 55. Even more preferably, the length of thestainless steel tubing is less than 10 cm. Reducing the tubing lengthdecreases the delay time to the reactor chamber 55. Reactor chamber 55can be a cold wall or hot wall reactor chamber. Most preferably reactorchamber 55 is maintained at a temperature equal to or greater than thehighest high temperature over zone used to entrain the reactants intoprocess gases 50. A bypass around reactor chamber 55 of the solid metalchloride or metal halide sources is also optionally disclosed. Withinreactor chamber 55 as previously disclosed one or more freestandingnitride veneers 52 are positioned within the process gas 50 and heatedvia IR lamps 49 and 54 or optional other heating means including but notlimited laser, heater elements, or other actinic radiation sources. Thinsusceptor 51 may be used to indirectly heat the freestanding nitrideveneers 52 or even more preferably the freestanding nitride veneers 52are directly heated. Process gases 50 exit the reactor chamber 55.Optionally, an additional ALD valve maybe used to allow forpressurization of the reactor chamber 55. Unlike conventional MOCVDreactors this reactor design can be used in full digital mode in thatreactants can be individually be sequenced into reactor chamber 55 on amillisecond time scale. This couple with millisecond temperatureresponse of the freestanding nitride veneers 52 and IR lamps 49 and 54is a preferred embodiment of this invention. Using this approach verydistinct interfaces can be created while maintain high growth rateswhich ultimately determine the process cycle time. The ability tointroduce process gases 50 from high vapor pressure metal chloride ormetal halide source in a fully digital mode is a preferred embodiment ofthis invention. The use of vacuum means to further evacuate reactorchamber 55 is disclosed. Most preferably an inert gas enclosuresurrounds this rapid thermal reactor for both safety and to furtherprevent any oxygen entrainment into the process gases 50 due to leakswithin the reactor.

FIG. 13 depicts a surface modified freestanding nitride veneer 56. Theformation of photonic crystal structure, micro-optics, gratings, andother optical structures on one or both veneer surfaces 57 and 58 isdisclosed. The formation of extraction elements on one or both veneersurfaces 57 and 58 is a preferred embodiment of this invention. Thesubsequent epitaxial overgrowth of devices over veneer surfaces 57and/or 58 to create embedded structures is disclosed. In this manner theactive region of DHJ, SQWs, MQWS and quantum dot devices can bemodified. Since freestanding nitride veneer 56 has a gallium rich sideand a nitrogen rich side veneer surfaces 57 and 58 maybe modified withthe same or different methods depending on subsequent process steps.

FIG. 14 depicts a freestanding nitride veneer 59 is which doped/modifiedvia ion implantation 60 and 61 on one or both sides of freestandingnitride veneer 59. The use of this technique to form a large areasemiconducting device is disclosed. Post processing to enhance diffusionand/or mitigate lattice damage is also disclosed.

FIG. 15 depicts a luminescent freestanding nitride veneer 63. In oneembodiment at least one luminescent element 65 is doped into luminescentfreestanding nitride veneer 63. At least one luminescent element 65maybe include but not limited to rare earths, Zn, Sn, Bi, Sb, Li, andother ions known in the art. Alternately or in combination with bulkdoping, luminescent freestanding nitride veneer 63 may be used as agrowth substrate for outer layers 62 and 64. The use of the crystalquality/nature, thermal conductivity, cleavability, high processingtemperature, and transmission characteristics of luminescentfreestanding nitride veneer 63 to form luminescent layers via but notlimited to sputtering, LPE, hydrothermal, melt processes, spin coating,evaporation, MOCVD, ALD, HYPE, MBE, and PECVD is disclosed. The use ofspin coating and high temperature thermal processing/anneal up to thedecomposition temperature of GaN to enhance the luminescent propertiesof outer layers 62 and 64 is preferred embodiment. The selection ofmaterials for outer layer 62 and 64 with refractive indices less thanluminescent freestanding nitride veneer 63 such that a waveguidingstructure is formed is disclosed. In this case, edge emission 67 can beenhanced. The use of dichroic coatings, photonic crystal structures, andor microoptical elements to restrict, modify, and/or block emission 71and 70 from the luminescent freestanding nitride veneer is disclosed.Excitation means 68 and 69 may be coupled into luminescent freestandingnitride veneer 63 outer layers 62 and 64. Alternately, excitation means68 and 69 may be coupled into the edges of luminescent freestandingnitride veneer 63.

FIG. 16 depicts a diode pumped laser formed using a freestanding nitrideveneer 73 as the gain media. The incorporation of luminescent elementsincluding but not limited to rare earths and Zn into freestandingnitride veneer 73 is disclosed. Alternately, the use of freestandingnitride veneer 73 as a growth substrate for formation of luminescentgain media layers 78 and/or 79 is also disclosed. In this case theoptical transmission, high thermal conductivity, cleavability, andlattice characteristics are important attributes of freestanding nitrideveneer 73. A preferred embodiment of this invention is the use offreestanding nitride veneer 73 as a cleavable gain media pumped via pumpdiodes 75 and 76. Output face 72 and reflector 74 can be used to createa laser cavity. Alternately the formation of disc and other non-linearcavities are also disclosed. The use of air and liquid cooling is alsodisclosed.

FIG. 17 depicts a nitride HEMT on freestanding nitride veneer 80. A widerange of device structures are possible for HEMTs, but the basic designinvolves active region 81 in which a 2 DEG is typically formed. Currentflow between Drain 83 and Source 82 is controlled via Gate 84 whichmodulates the current flow in region 85. The 2 DEG is typically formedbetween AlGaN and GaN layers in active region 81. The use offreestanding nitride veneer 80 enables the creation of higher qualitylayers and lower overall device thermal impedance as compared tosilicon, sapphire, and SiC template approaches. A preferred embodimentis the formation of high quality high aluminum content AlGaN layers onfreestanding nitride veneer 80 for use in active region 81. Alsodisclosed is the formation of dual sided devices in which drain 83 andsource 82 are formed on opposite sides of active region 81. Alternatelythe formation of Gate 84 on the opposite side of active region 81 aseither and/or both drain 83 and source 82 is an also an embodiment ofthis invention. The use of dual sided contacts in 3 Dimensional devicesis a preferred embodiment. The use of dual sided contacts to reducesurface electron states between gate 84 and drain 83 and/or source 82 isalso disclosed. The formation of at least one recessed gate 84 on eitherside of active region 81 is a preferred embodiment of this invention.

FIG. 18 depicts a 3 dimensional stack of freestanding nitride veneerbased devices 92, 93, and 94. Because the devices are all nitride bothsides of the devices are available for contacts, heatsinking and devicegrowth. Interconnects 87 may consist of but not limited to ball bumps,copper slugs, solder, phase change materials, as well as otherinterconnect means as known in the art. The devices maybe partially orfully bonded together via adhesive layer 88 which may consist ofinorganic and/or organic bonding materials. Alternately, the spacebetween the devices maybe used as a fluid pathway with an inlet flow andan exit flow 92. Heatsinks 90 and 91 can be used to thermally conductheat out the 3 dimensional stack as well as provide a means of directingcooling fluids and/or gases into the device. The case where at least oneof the freestanding nitride based devices 92, 93, and 94 contains atleast one light emitting device 86 which may be used for irradiation,communication, sensing, and/or displays is a preferred embodiment ofthis invention.

FIG. 19 depicts a heatpipe 96 to which a flexible freestanding device 95is mounted. The ability to mount to a cylindrical surface not onlyreduces additional steps in forming the heatpipe but also allows theflexible freestanding device 95 to operate in a non flat manner. Thismay be advantageous for enhanced light extraction, reduced stresses,and/or better optical fixture design.

FIG. 20 depicts a integrated biosensor based on a freestanding nitrideveneer 100. The inherent transparency and ability to grow both emittersand detectors on a single layer enables the freestanding nitride veneer100 to create a fully integrated biosensor. The biosensor detectsoptical changes in the bio-layer 98. Typically a index matching layer 99is used to effectively couple light within the freestanding nitrideveneer 100 into bio layer 98. Light generated by source 105 is coupledinto the freestanding nitride veneer 100 via coupling layer 104.Coupling layer 104 can be used to restrict the angular, wavelengthand/or polarization of the light rays 102 which enters the freestandingnitride veneer 100. In a similar manner coupling layer 101 can limit theangular, polarization, and/or wavelength with enters detector 103. Inthis manner the sensitivity of the device can be enhanced allowing fortarget molecules 97 can be detected by the bio layer 98.

While the invention has been described in conjunction with specificembodiments and examples, it is evident to those skilled in the art thatmany alternatives, modifications and variations will be apparent inlight of the foregoing description. Accordingly, the invention isintended to embrace all such alternatives, modifications and variationsas fall within the spirit and scope of the appended claims.

1. (canceled)
 2. (canceled)
 3. (canceled)
 4. (canceled)
 5. (canceled) 6.(canceled)
 7. A method for fabricating a flexible single crystal nitrideveneer comprising: harvesting a single crystal nitride layer grown onsubstrate by laser lift off; wherein said single crystal nitride layerhas a thickness between 20 and 150 μms; and using rapid thermalprocessing to deposit a semiconductor layer onto at least one side ofsaid single crystal nitride layer.
 8. The method of claim 7 wherein thesingle crystal nitride veneer growth substrate is flexed during growthof said at least one semiconductor layer to enhance the growth and/orphysical properties of said semiconductor layer.
 9. The method of claim7 to fabricate a single crystal nitride veneer layer wherein said atleast one semiconductor layer consists of at least one of the followingmaterials: silicon, silicon/germanium, germanium, gallium arsenide,alingap, dilute nitrides, InP, antinomides, and ZnO alloys.
 10. Themethod of claim 7 to fabricate a single crystal nitride veneer layerwherein said semiconductor layer is deposited on said single crystalnitride veneer using at least one of the following methods: sputtering,LPE, MBE, MOCVD, HYPE, ALD, evaporation, spraying, dip coating,printing, and/or spin coating.
 11. The method of claim 7 to fabricate asingle crystal nitride veneer layer wherein said semiconductor layer isa nitride solar cell junction.
 12. The method of claim 7 to fabricate asingle crystal nitride veneer layer wherein said method can form of atleast one of the following devices: laser diode, HEMT, solid statepumped laser diode, solar cell, LED, or biosensor.